Light-emitting apparatus, phosphor, and method of producing it

Abstract

A light-emitting apparatus composed of a light source that emits primary light and a phosphor that absorbs the primary light and emits secondary light offers high brightness, low power consumption, and a long lifetime while minimizing adverse effects on the environment. The phosphor is formed of a III–V group semiconductor in the form of fine-particle crystals each having a volume of 2 800 nm 3 or less. The light emitted from the fine-particle crystals depends on their volume, and therefore giving the fine-particle crystals a predetermined volume distribution makes it possible to adjust the wavelength range of the secondary light.

1. A light-emitting apparatus comprising:
 a light source that emits primary light; 
 a phosphor formed as fine-particle crystals of a III–V group compound semiconductor, the fine-particle crystals being nano-crystals each having a volume of 2800 nm 3  or less: and 
 a phosphorescent portion formed by combining the phosphor with a transparent member, 
 wherein the phosphorescent portion receives the primary light emitted from the light source directly with the primary light unscattered in an optical path therebetween so that the phosphor absorbs at least part of the primary light and emits secondary light having a longer peak wavelength than the primary light. 
 
     
     
       2. A light-emitting apparatus as claimed in  claim 1 ,
 wherein of the III group elements and V group elements contained in the III–V group compound semiconductor, 50% or more of the III group elements is indium, and 95% or more of the V group elements is nitrogen. 
 
     
     
       3. A light-emitting apparatus as claimed in  claim 1 , wherein
 the phosphorescent portion has a multilayer structure in which a volume distribution of the nano-crystals varies unilaterally from an entrance side to an exit side of the primary light, and the phosphorescent portion emits the secondary light having a wavelength distribution corresponding to the volume distribution. 
 
     
     
       4. A light-emitting apparatus as claimed in  claim 1 ,
 wherein the III–V group compound semiconductor is a nitride semiconductor, and the nano-crystals thereof are each composed of a single portion having a uniform energy band gap. 
 
     
     
       5. A light-emitting apparatus as claimed in  claim 1 ,
 wherein the III–V group compound semiconductor is a nitride semiconductor, and the fine particle crystals nano-crystals thereof are each composed of a first portion and a second portion that encloses the first portion and that has a greater energy band gap than the first portion. 
 
     
     
       6. A light-emitting apparatus as claimed in  claim 1 ,
 wherein, as the phosphorescent portion, the nano-crystals of the III–V group compound semiconductor are dispersed in glass, and the peak wavelength of the primary light emitted from the light source is in a range from 380 nm to 500 nm, both ends inclusive. 
 
     
     
       7. A light-emitting apparatus as claimed in  claim 1 ,
 wherein, as the phosphorescent portion, the nano-crystals of the III–V group compound semiconductor are dispersed in resin, and the peak wavelength of the primary light emitted from the light source is in a range from 395 nm to 500 nm, both ends inclusive. 
 
     
     
       8. A light-emitting apparatus as claimed in  claim 1 ,
 wherein, in an optical path from the light source to the phosphorescent portion, a filter is provided that cuts off light of wavelengths shorter than 395 nm. 
 
     
     
       9. A light-emitting apparatus as claimed in  claim 1 ,
 wherein, opposite to a side of the phosphorescent portion to which the primary light enters and in an optical path of the secondary light emitted from the phosphor, a filter for cutting off only the primary light that passes through the phosphorescent portion is provided. 
 
     
     
       10. A light-emitting apparatus as claimed in  claim 1 ,
 wherein the light source includes a light-emitting device using a nitride-based Ill-V group compound semiconductor. 
 
     
     
       11. A light-emitting apparatus comprising:
 a light source that emits primary light; 
 a phosphor formed as fine-particle crystals of a III–V group compound semiconductor, the fine-particle crystals being nano-crystals each measuring 14 nm or less in two directions perpendicular to a longest side thereof; and 
 a phosphorescent portion formed by combining the phosphor with a transparent member, 
 wherein the phosphorescent portion receives the primary light emitted from the light source directly with the primary light unscattered in an optical path therebetween so that the phosphor absorbs at least part of the primary light and emits secondary light having a longer peak wavelength than the primary light. 
 
     
     
       12. A light-emitting apparatus as claimed in  claim 11 , wherein, of III group elements and V group elements contained in the III–V group compound semiconductor, 50 % or more of the III group elements is indium, and 95 % or more of the V group elements is nitrogen. 
     
     
       13. A light-emitting apparatus as claimed in  claim 11 ,
 wherein 
 the phosphorescent portion has a multilayer structure in which a volume distribution of the nano-crystals varies unilaterally from an entrance side to an exit side of the primary light, and the phosphorescent portion emits the secondary light having a wavelength distribution corresponding to the volume distribution. 
 
     
     
       14. A light-emitting apparatus as claimed in  claim 11 ,
 wherein the III–V group compound semiconductor is a nitride semiconductor, and the nano-crystals thereof are each composed of a single portion having a uniform energy band gap. 
 
     
     
       15. A light-emitting apparatus as claimed in  claim 11 ,
 wherein the III–V group compound semiconductor is a nitride semiconductor, and the nano-crystals thereof are each composed of a first portion and a second portion that encloses the first portion and that has a greater energy band gap than the first portion. 
 
     
     
       16. A light-emitting apparatus as claimed in  claim 11 ,
 wherein, as the phosphorescent portion, the nano-crystals of the III–V group compound semiconductor are dispersed in glass, and the peak wavelength of the primary light emitted from the light source is in a range from 380 nm to 500 nm, both ends inclusive. 
 
     
     
       17. A light-emitting apparatus as claimed in  claim 11 ,
 wherein, as the phosphorescent portion, the nano-crystals of the III–V group compound semiconductor are dispersed in resin, and the peak wavelength of the primary light emitted from the light source is in a range from 395 nm to 500 nm, both ends inclusive. 
 
     
     
       18. A light-emitting apparatus as claimed in  claim 11 ,
 wherein, in an optical path from the light source to the phosphorescent portion, a filter is provided that cuts off light of wavelengths shorter than 395 nm. 
 
     
     
       19. A light-emitting apparatus as claimed in  claim 11 ,
 wherein, opposite to a side of the phosphorescent portion to which the primary light enters and in an optical path of the secondary light emitted from the phosphor, a filter for cutting off only the primary light that passes through the phosphorescent portion is provided. 
 
     
     
       20. A light-emitting apparatus as claimed in  claim 11 ,
 wherein the light source includes a light-emitting device using a nitride-based III–V group compound semiconductor.